BERLIN (AP) — The European Space Agency plans to remotely update the software on its Mars Express probe to ensure the aging spacecraft remains stable.

The probe arrived at Mars in late 2003 for a two-year mission , but almost 15 years later it's still operating.

ESA said Wednesday four of Mars Express' six gyroscopes — used to measure the probe's rotation — are failing, which would end the mission in 2019.

So engineers decided to rewrite the spacecraft's computer code so it can orient itself using pictures of surrounding stars most of the time. The code was uploaded last Sunday. A reboot is planned Monday.

While similar patches have been developed for other spacecraft, mission manager Patrick Martin said "this is certainly the most complex and extensive software rewrite we've done in recent memory."